Colour pickup tube having a false signal preventing film

ABSTRACT

In a vidicon type pickup tube for use in single tube type or two tube type colour television camera systems comprising a transparent glass window, an optical colour analyzing stripe filter formed on one surface of the glass window, and a false signal preventing film made of a layer of transparent solid substance and formed on the surface of the stripe filter, the false signal preventing film extends to a given extent beyond or terminates short of the periphery of the stripe filter.

United States Patent Nobutoki 3,772,552 11/1973 Kubota ..3l3/390X [75]lnventor: Samuro Nobutoki, Mobara, Japan Primary Examiner siegfriedGrimm 73 Assignee; Hitachi Ltd Tokyo, japan Attorney, Agent, orFirm-Charles E. Pfund, Esq.

[22] Filed: Mar. 6, 1974 [21] Appl. No.: 448,460

[57] ABSTRACT [30] Foreign Application Priority Data In a vidicon typepickup tube for use in single tube Apr. 11, 1973 Japan 48-40456 type ortwo tube type 01 ur television camera tems comprising a transparentglass window, an opti- [52] US. Cl. 313/371; 313/388; 313/390 cal colouranalyzing stripe filter formed on one sur- [51] Int. C1. H01J 29/36 faceof the glass window, and a false signal preventing Field of Seal'dl filmmade of a layer of transparent solid substance and 390 formed on thesurface of the stripe filter, the false signal preventing film extendsto a given extent beyond [56] References Cited or terminates short ofthe periphery of the stripe filter.

UNITED STATES PATENTS 3,026,416 3/ 1962 Weimer 313/371 X 12 Claims, 23Drawing Figures 6 5 7 3 E31 I 2 1 4 I I l l| t l I: v 1 1 U l Sheet 1 of6 US. Patent Oct. 14, 1975 Fla/- Sheet 2 of 6 3,912,962

U.S. Patent Oct. 14, 1975 F/G.3 m BAR am am US. Patent Oc't." 14, 1975Sheet 3 of6 3,912,962

)oma 5 14a- (C) 5 mimw (d) ma; 5 BBB 15a BAR EBB U.S. Patent Oct.14,1975Sheet4of6 3,912,962

F/G.8A F7683 U .S. Patent Got. 14, 1975 Sheet 5 of6 3,912,962

F/G./0B

F/G./0c

U.S. Patent Oct. 14,1975 Sheet6of6 3,912,962

F/G.//A

F/G.//B

COLOUR PICKUP TUBE HAVING A FALSE SIGNAL PREVENTING FILM BACKGROUND OFTHE INVENTION This invention relates to a pickup tube for use in singletube type or two tube type colour television camera systems (hereinaftermerely referred to as a filter encoded pickup tube) and moreparticularly to a vidicon type pickup tube in which an optical colouranalyzing stripe filter is provided on one side surface of a transparentglass window.

Among pickup tubes of the type including an optical colour analyzingstripe filter may be mentioned the filter encoded pickup tubes. Thefilter encoded pickup tube is provided with an optical colour analyzingstripe filter on the rear surface of a transparent glass window directedto an object, and a transparent electroconductive film and aphotoconductive film which are laminated on the stripe filter. In thiscase, the optical colour analyzing stripe filter comprises two filtercomponents, one of them including an alternate arrangement of a filterelement provided with fine stripes transmitting light of substantiallyall colours from the object and a filter element provided with finestripes essentially preventing transmission of red light among light ofvarious colours from the object. The other filter component includes analternate arrangement of a filter element provided with fine stripestransmitting light of substantially of all colours from the object and astripe element provided with fine stripes essentially preventingtransmission of blue light among light of various colours from theobject. These two filter components are superposed one upon the othersuch that respective filter elements of the former filter componentintersect at an angle with the respective filter elements of the latterfilter component so as to decrease beats caused by these two fine stripefilters.

With this construction, the light image of the object projected upon thephotoconductive film through the transparent glass window is sampled ata spatial frequency of the optical colour analyzing stripe filter sothat when the light image is scanned with an electron beam, a multiplexcolour signal is produced having two carrier waves caused by thedifference in the spacing between the filter element that blocks the redlight and the filter element that blocks the blue light of said twofilter components. By separating the colour signal by means of onelowpass filter and two bandpass filters it is possible to produce green,red and blue signals corresponding to the three primary colours oflight.

Where such optical colour analyzing strip filter comprises a dichroicfilter generally formed by vapour desposition technique, for example,since the thickness of the dichroic filter is of the order of 1 micronthe thickness of the portion where two filters are superposed one uponanother amounts to a maximum of about 3 microns with the result that thesurface of the glass plate on which the optical colour analyzing stripefilter is formed becomes irregular. If the transparent electroconductivefilm and the photoconductive film were formed directly on such anirregular surface these films would also be irregular. When such anirregular photoconductive film is incorporated into a colour pickup tubean abnormal condition of the signal current will result due to anabnormal surface electric field corresponding to the irregularity of thepickup surface. Consequently, foreign substances deposited on thedichroic filter of delicate construction and on the irregular surfaceimpair the photoconductive film thereby degrading its photoelectricconversion characteristic with the result that false image signal willbe produced corresponding to the irregularity of the image pickupsurface. Thus, various troubles such as the false colour signal arecaused in the operation of the image pickup tube.

For the purpose of eliminating or decreasing the defects described wehave already proposed an improved construction in which the opticalcolour analyzing stripe filter is coated with a false signal preventingfilm consisting of a layer of transparent solid substance such as aglass layer or a Si0 layer so as to eliminate the irregularity on thesurface of the optical colour analyzing stripe filter. If desired, thesurface of the filter is made more flat by polishing, chemical etching,or the polishing and chemical etching in combination. By this means, itwas possible to make substantially fiat and smooth the transparentconductive film and the photoconductive film which are formed on thecoated layer.

However, where a pickup tube is provided with an image pickup platecoated with such a false signal preventing film, it was found that incertain cases it is impossible to read out the signal current, and thatsuch fault is caused by the exfoliation of the false signal preventingfilm or the cracking thereof which are caused by the heat treatment atthe time of forming the NESA film.

More particularly, in the vidicon type colour pickup tube it isnecessary to form a transparent conductive film on the inner surface ofthe transparent glass window so as to derive out the signal produced inthe photoconductive film and to permit the incident rays to reach thephotoconductive surface. Usually, a so-called NESA film is used as thetransparent conductive film.

The NESA film consists essentially and mainly of tin oxide prepared byspraying onto a glass substrate a fine spray of a solution containing asolute consisting essentially of stannic chloride and then decomposingand oxidizing the stannic chloride. To form the film it is essential toheat the glass substrate at a temperature of about 500C so that due tothe difference in the coefficient of thermal expansion of a structureformed on the glass substrate and the false signal preventing filmapplied onto the structure there is a tendency of peeling off the falsesignal preventing film or cracking thereof. For this reason, the NESAfilm also tends to peel off or crack.

SUMMARY OF THE INVENTION It is an object of this invention to eliminatesuch defects.

The formation of the peel off and cracks of the false signal preventingfilm on the substrate which are caused by the difference in thecoefficient of thermal expansion depends upon the state of twodimensional spreading of the film on the surface of the glass substrate.More particularly, when the film is formed on the portion of the faceplate of the pickup tube where the optical colour analyzing stripefilter is disposed or extends in a predetermined area of the mirrorsurface of the transparent glass window of the pickup tube, it wasconfirmed that there is no peeling off and cracking of the false signalpreventing film caused by the heat treatment of the NESA film. It isbelieved that the coarse or irregular surface of the optical colouranalyzing stripe filter functions to prevent the peeling off of thefalse signal prevenang film. It is also believed that the peeling offand cracking of the false signal preventing film can be precluded bydecreasing the area in which the film extends on the glass mirrorsurface, thereby correspondingly decreasing the adhering area by a smallbonding force between the film and the mirror surface.

Accordingly, the vidicon type colour pickup tube of this invention ischaracterized in that it comprises an optical colour analyzing stripefilter formed on the rear surface of a transparent glass window, and afalse signal preventing film of a transparent solid substance and formedon the rear surface of the optical colour analyzing stripe filter andthat the false signal preventing film is formed to extend to a mirrorsurface in a predetermined area of the transparent glass window or notto extend to the mirror surface of the transparent glass window.

BRIEF DESCRIPTION OF THE DRAWINGS Further objects and advantages of theinvention will become apparent from the following detailed descriptiontaken in conjunction with accompanying drawings in which:

FIG. 1 is a diagrammatic representation of one example of a vidicon typepickup tube;

FIG. 2 is a perspective view of an optical colour analyzing stripefilter;

FIG. 3. is a diagram showing an actual construction of the opticalcolour analyzing stripe filter;

FIG. 4 is a perspective view of the optical colour analyzing stripefilter shown in FIG. 3;

' FIGS. 5a and 5b are partial sectional views showing certain steps ofpreparing the colour analyzing stripe filter;

FIGS. 6a through 6d show examples of the relationship between theoptical colour analyzing stripe filter and the false signal preventingfilm;

FIGS. 7a, 7b and 7c are partial sectional views showing different typesof the combinations of the optical colour analyzing stripe filter andthe false signal preventing film;

FIG. 8A shows a plan view of one embodiment of the pickup tube of thisinvention;

FIG. 8B is a sectional view of the pickup tube shown in FIG. 8A takenalong a line VIIIB-VIIIB;

FIG. 9A shows a plane view of another embodiment of the pickup tube ofthis invention;

FIG. 9B is a sectional view of the pickup tube shown in FIG. 9A takenalong a line IXB-IXB;

FIG. 10A shows a plan view of still another embodiment of the pickuptube of this invention;

FIGS. 10B and 10C are sectional views of the pickup tube shown in FIGS.10A taken along lines XBXB and XCXC, respectively;

FIG. 11A shows a plan view of yet another embodiment of the pickup tubeembodying the invention and FIGS. 11B and 11C are sectional views of thepickup tube shown in FIG. 11A taken along lines XIBXIB and XICXIC,respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction of a filterencoded pickup tube will firstly be described with reference to FIG. 1of the accompanying drawing. The pickup tube 1 illustrated thereincomprises an electron gun 2, a focusing coil 3,

a deflection coil 4, a transparent glass window 5, an optical colouranalyzing stripe filter 5, a transparent electroconductive film 7, aphotoconductive film 8, anda signal take out terminal 9 connected to thetransparent conductive film 7. An optical system is designated by a lens10 and the locus of the electron beam emitted by the electron gun 2 isdesignated by 11. The optical colour analyzing stripe filter 6 comprisesa dichroic filter including an alternate lamination of the layers oftitanium dioxide TiO and silicon dioxide SiO for example, and includestwo filter components 6A and 68, as shown in FIG. 2. One component 6Aincludes an alternate arrangement of stripe filter elements 6AWtransmitting light of substantially all colours from an object, notshown, and stripe filter elements 6AR blocking the red light. Filterelements 6AW and 6AR have the same width DR. The other stripe filtercomponent 63 includes a similar alternate arrangement of stripe filterelements 6BW transmitting light of substantially all colours and stripefilter elements 688 blocking blue light. Again, stripe filter elements6BW and 6B8 have the same width DB. Widths DR and DB should bedifferent, and in FIG. 2, DB is shown narrower than DR.

While in FIG. 2, the stripe filter elements 6AR, 6AW and 6BB, 6BW,of twofilter components 6A and 6B are shown parallel with each other,actually, however, these two groups of the stripe filter elementsintersect each other at a certain angle as shown in FIG. 3 so as todecrease the beats caused by these two groups.

One example of the actual construction of the optical colour analyzingstripe filter 6 is shown in FIGS. 4 and 5. More particularly, onlystripe filter elements 6AR of the filter element 6A which substantiallyblock red light are formed on the glass window 5 (see FIG. 5b) andthereafter the stripe filter elements 688 of the other filter component68 which substantially block the blue light are formed on the stripefilter elements 6AR without forming the stripe filter elements 6AW and6BW of the filter components 6A and 63, respectively, which transmit thelight of all colours, as shown in FIG. 5a. According to this invention,for the purpose of eliminating or alleviating the surface irregularityof the optical colour analyzing stripe filter as shown in FIGS. 4 and5a, thus eliminating the generation of the false signals, false signalpreventing films consisting of a glass layer or a SiO layer are appliedas shown by 12 in FIG. 6a, and polished or etched to form a smoothsurface 12a in FIG. 6b. A similar film 13 applied as shown in FIG. 6c ispolished or etched as shown at 13a in FIG. 6d. In particular afterforming one type of the stripe filter element 6AR on the glass substrate5, the false sig nal preventing film 13 is applied thereon as shown inFIG. 6c and polished or etched as shown in FIG. 6d. Thereafter alternatelayers of the stripe filter element 633 as shown in FIG. 7c and thefalse signal preventing film 15 as shown in FIG. 7a, are repeatedlyformed on the resulting assembly and finished products havingsubstantially flat and smooth surfaces 14a, and 15 a as shown in FIGS.7b and 7c are produced by polishing or chemically etching the surfaces,or the polishing and chemical etching in combination.

FIGS. 8 through 11 show different constructions of the false signalpreventing films embodying the invention. Thus, in the constructionshown in FIGS. 8A and 88, one or more types of the groups of the opticalcolour analyzing stripe filters are arranged in parallel or crosssuperposition relationship on one side surface of the transparent glasswindow 5 whose peripheral edge is vacuum sealed to the tube. A circulararea 16 where the optical colour analyzing stripe filter 6 is coated(hereinafter referred to as a filter coated area 16) is provided, whichof course contains the effective image pickup region 29 of therectangular configuration of the pickup tube, and a false signalpreventing film 18 of a layer of transparent solid substance such as aglass layer or a SiO layer is applied in concentric with the filtercoated area 16, an area 17 of the film 18 (hereinafter referred to as afilm coated area 17) having larger diameter than the filter coated area16. It was found that if the length of the extension I of the filmcoated area 17 beyond the filter coated area 16 is limited to be equalto or less than about 5 mm, the false signal preventing film 18 wouldnever peel off and/or crack. With the length of the extension I largerthan 5 mm, the peel ing off and/or cracking is encountered. In otherwords, when the bonding surface between the false signal preventing film18 and the mirror surface of the transparent glass window 5 is limitedto an annular surface having a maximum width of about 5 mm it ispossible to prevent the peeling off and/or the cracking of the falsesignal preventing film, owing to the bonding force between the film andthe irregular surface of the optical colour analyzing stripe filter.

FIGS. 9A and 9B show another example of the pickup tube embodying theinvention. In this embodiment, the film coated area 17 is made smallerthan the filter coated area 16 on which the optical colour anacoatedarea 17 is made to be equal to or a little larger than the effectiveimage pickup region 19, thus leaving exposed the annular portion of thefilter coated area 16 about the film 18. It was confirmed that thisconstruction also effectively prevents peeling off and/or cracking ofthe false signal preventing film 18. Again, it is preferable to limitthe width of the annular portion to be equal to or less than 5 mm.

In FIGS. 8A and 88, an embodiment has been described wherein the filmcoated area l7 extends beyond the periphery of the filter coated area 16and in FIGS. 9A and 98 another embodiment has been described wherein thefilm coated area 17 is contained within the filter coated area 16. Itshould be understood, however, that the film coated area 17 may be soformed as to irregularly intersect the periphery of the filter coatedarea 16. In other words, the periphery of the film coated area 17 may beconfined in a region defined by the outward extension of 5 mm from theperiphery of the filter coated area 16 and the inward spacing of 5 mmfrom the periphery of the filter coated area 16, the region having thewidth equal to 10 mm.

FIGS. 10A, 10B and 10C illustrate still another embodiment of the novelpickup tube of this invention. In this modification, a peripheralcoating layer made of a different or same material as the stripe filter6 which is formed in a rectangular filter coated area 16 and of amaterial different from that of the false signal preventing film 18 isformedto surround the area 16. The area of the peripheral coating layer20 is hereinafter referred to a layer area 21. In this example, theeffective image pickup region 29 is also rectangular and contained inthe area 16. In this manner, the peripheral coating layer 20 is formedindependently of the optical colour analyzing stripe filter 6 tosurround the same such that the film coated area 17 covers the filterlyzing stripe filter is formed. For example, the film coated area 16 andextends beyond the layer area 21 with an extension I. The extension I isof a maximum width of less than about 5 mm.

FIGS. 11A, 11B and 11C show another embodiment of this invention,wherein the film coated area 17 covers filter coated area 16 and iscontained within the layer area 21, leaving exposed an extension I ofthe same. In this case too, it is advantageous to limit the extension lto be less than about 5 mm. In FIGS. 10A, 10B and 10C, still anotherembodiment has been described wherein the film coated area 17 extendsbeyond the periphery of the layer area 21 and in FIGS. 11A, 11B and 11Cfurther embodiment has been described wherein the periphery of the filmcoated area 17 is contained within the layer area 21. However, it shouldbe understood that the film coated area 17 may be so formed as toirregularly intersect the periphery of the layer area 21. In otherwords, the periphery of the film coated area 17 may be confined in aregion defined by the outward extension of 5 mm from the periphery ofthe layer area 21 and the inward spacing of 5 mm from the periphery ofthe layer area 21, the region having the width equal to 10 mm. In theembodiments shown in FIGS. 8 through 11, the filter coated area 16 showsa region in which two types of the optical colour analyzing stripefilters are arranged in crossed and superposed relationship as shown inFIG. 4 or only one type of the optical colour analyzing stripe filter isarranged as shown in FIG. 5b, and only the effective pickup region 19,in this area 16, is used to prevent the generation of the false signals,so that the configuration of the area 16 is not necessarily be limitedto circular or rectangular as illustrated in these figures. The same istrue for the peripheral coating layer 20.

' As has been described hereinabove, in accordance with this invention,in order to prevent peeling off and- /or cracking of the false signalpreventing film 18, an optical colour analyzing stripe filter in theform of the interference filter coating is formed on a glass substrate,and the false signal preventing film 18 having a diameter larger orsmaller by less than 5 mm than that of the filter is formed. However, itshould be understood that the film firstly formed on the glass substrateshould not always be constituted by a dichroic filter but may be formedof a substance different from the false signal preventing film and thatthe filter film should not always be constituted by parallel stripes. Itwas found that any other configurations of the filter such as a wire netor spots can also effectively prevent the peeling off and/or cracking ofthe false signal preventing film provided that the filter has a suitablepercentage surface area, with respect to the area of false signalpreventing film arrangement, configuration and dimension equivalent tothose of 6AR and 6BB shown in FIG. 4.

Thus, according to this invention, by specifying the area in which thefalse signal preventing film is formed it is possible to prevent thepeeling off and/or cracking of the film and hence the peeling off and/orcracking of the transparent conductive film caused by such peeling offand/or cracking of the false signal preventing film, as well as thedecrease in the conductivity of the transparent conductive film.

What is claimed is:

1. In a colour vidicon type pickup tube for use in single tube type ortwo tube type colour television camera systems comprising a transparentglass window, an optical colour analyzing stripe filter formed on therear surface of said glass window, and a false signal preventing filmmade of a layer of transparent solid substance and formed on the surfaceof said filter, the improvement wherein said false signal preventingfilm is formed in such a manner that the periphery of said false signalpreventing film is confined in a region defined by an outward extensionof mm from the periphery of said optical colour analyzing stripe filterand an inward spacing of 5 mm from the periphery of the same, saidoutward extension not touching the vacuum sealed portion of said glasswindow.

2. The pickup tube according to claim 1 wherein said false signalpreventing film extends beyond the periphery of said optical colouranalyzing stripe filter by a length of less than 5 mm.

3. The pickup tube according to claim 1 wherein said false signalpreventing film covers a portion of an area in which said optical colouranalyzing stripe filter is formed, said portion being spaced from theouter periphery of said area by a length of less than about 5 mm.

4. In a colour vidicon type pickup tube for use in single tube type ortwo tube type colour television camera systems comprising a transparentglass window, an optical colour analyzing stripe filter formed on therear surface of said glass window, a false signal preventing film madeof a layer of transparent solid substance and formed on the surface ofsaid filter, and a peripheral coating layer formed to surround theperiphery of said optical colour analyzing stripe filter, theimprovement wherein said false signal preventing film is formed in sucha manner that it covers said optical colour analyzing stripe filter andsaid peripheral coating layer and that the periphery of said falsesignal preventing film is confined in a region defined by an outwardextension of 5 mm from the periphery of said peripheral coating layerand an inward spacing of 5 mm from the periphery of the same, saidoutward extension not touching the vacuum sealed portion of said glasswindow.

5. The pickup tube according to claim 4 wherein said false signalpreventing film extends beyond the periphery of said peripheral coatinglayer by a length of less than 5 mm.

6. The pickup tube according to claim 4 wherein said peripheral coatinglayer is made of a substance which is the same as that comprising atleast a portion of said optical colour analyzing stripe filter.

7. The pickup tube according to claim 4 wherein said peripheral coatinglayer is made of a material containing a substance from which at least aportion of said optical colour analyzing stripe filter is made of.

8. The pickup tube according to claim 4 wherein said peripheral coatinglayer is made of a substance different from that of said false signalpreventing film.

9. The pickup tube according to claim 4 wherein said false signalpreventing film covers a portion of said peripheral coating layer andterminates less than 5 mm short of the outer periphery of saidperipheral coating layer.

10. The pickup tube according to claim 1 wherein the surface of saidfalse signal preventing film is treated by a step selected from thegroup consisting of being polished, chemically etched or subjected topolishing and chemical etching in combination to form a flat and smoothsurface.

1 1. The pickup tube according to claim 4 wherein the surface of saidfalse signal preventing film is treated by a step selected from thegroup consisting of being polished, chemically etched or subjected topolishing and chemical etching in combination to form a flat and smoothsurface.

12. The pickup tube according to claim 8 wherein the surface of saidfalse signal preventing film is treated by a step selected from thegroup consisting of being polished, chemically etched or subjected topolishing and chemical etching in combination to form a flat and smoothsurface.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIONPATENT NO. I 3,912,962 DATED October 14, 1975 lN\ ENTOR(S) SaburoNobutoki It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Column 4, line 2, "filter 5" should read filter 6 Colunm 5, line 6,"region 29" should read region 19 Column 5, line 63, "region 29" shouldread region 19 Signed and Sealed this Ninth Day Of November 1976 [SEAL]Arrest:

RUTH C. MA SON C. MARSHALL DANN Amsrmx ()j/rcer (ummissmm'r ufPalenlsand Trademarks

1. In a colour vidicon type pickup tube for use in single tube type ortwo tube type colour television camera systems comprising a transparentglass window, an optical colour analyzing stripe filter formed on therear surface of said glass window, and a false signal preventing filmmade of a layer of transparent solid substance and formed on the surfaceof said filter, the improvement wherein said false signal preventingfilm is formed in such a manner that the periphery of said false signalpreventing film is confined in a region defined by an outward extensionof 5 mm from the periphery of said optical colour analyzing stripefilter and an inward spacing of 5 mm from the periphery of the same,said outward extension not touching the vacuum sealed portion of saidglass window.
 2. The pickup tube according to claim 1 wherein said falsesignal preventing film extends beyond the periphery of said opticalcolour analyzing stripe filter by a length of less than 5 mm.
 3. Thepickup tube according to claim 1 wherein said false signal preventingfilm covers a portion of an area in which said optical colour analyzingstripe filter is formed, said portion being spaced from the outerperiphery of said area by a length of less than about 5 mm.
 4. In acolour vidicon type pickup tube for use in single tube type or two tubetype colour television camera systems comprising a transparent glasswindow, an optical colour analyzing stripe filter formed on the rearsurface of said glass window, a false signal preventing film made of alayer of transparent solid substance and formed on the surface of saidfilter, and a peripheral coating layer formed to surround the peripheryof said optical colour analyzing stripe filter, the improvement whereinsaid false signal preventing film is formed in such a manner that itcovers said optical colour analyzing stripe filter and said peripheralcoating layer and that the periphery of said false signal preventingfilm is confined in a region defined by an outward extension of 5 mmfrom the periphery of said peripheral coating layer and an inwardspacing of 5 mm froM the periphery of the same, said outward extensionnot touching the vacuum sealed portion of said glass window.
 5. Thepickup tube according to claim 4 wherein said false signal preventingfilm extends beyond the periphery of said peripheral coating layer by alength of less than 5 mm.
 6. The pickup tube according to claim 4wherein said peripheral coating layer is made of a substance which isthe same as that comprising at least a portion of said optical colouranalyzing stripe filter.
 7. The pickup tube according to claim 4 whereinsaid peripheral coating layer is made of a material containing asubstance from which at least a portion of said optical colour analyzingstripe filter is made of.
 8. The pickup tube according to claim 4wherein said peripheral coating layer is made of a substance differentfrom that of said false signal preventing film.
 9. The pickup tubeaccording to claim 4 wherein said false signal preventing film covers aportion of said peripheral coating layer and terminates less than 5 mmshort of the outer periphery of said peripheral coating layer.
 10. Thepickup tube according to claim 1 wherein the surface of said falsesignal preventing film is treated by a step selected from the groupconsisting of being polished, chemically etched or subjected topolishing and chemical etching in combination to form a flat and smoothsurface.
 11. The pickup tube according to claim 4 wherein the surface ofsaid false signal preventing film is treated by a step selected from thegroup consisting of being polished, chemically etched or subjected topolishing and chemical etching in combination to form a flat and smoothsurface.
 12. The pickup tube according to claim 8 wherein the surface ofsaid false signal preventing film is treated by a step selected from thegroup consisting of being polished, chemically etched or subjected topolishing and chemical etching in combination to form a flat and smoothsurface.